linux-ext4 - Re: [PATCH v2 3/4] ext4: factor out write end code of inline file

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Date:   Fri, 16 Jul 2021 12:08:20 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, yukuai3@...wei.com
Subject: Re: [PATCH v2 3/4] ext4: factor out write end code of inline file

On Fri 16-07-21 11:56:06, Zhang Yi wrote:
> On 2021/7/15 20:08, Jan Kara wrote:
> > On Thu 15-07-21 09:54:51, Zhang Yi wrote:
> >> Now that the inline_data file write end procedure are falled into the
> >> common write end functions, it is not clear. Factor them out and do
> >> some cleanup. This patch also drop ext4_da_write_inline_data_end()
> >> and switch to use ext4_write_inline_data_end() instead because we also
> >> need to do the same error processing if we failed to write data into
> >> inline entry.
> >>
> >> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> > 
> > Just two small comments below.
> > 
> >> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
> >> index 28b666f25ac2..3d227b32b21c 100644
> >> --- a/fs/ext4/inline.c
> >> +++ b/fs/ext4/inline.c
> > ...
> >> +out:
> >> +	/*
> >> +	 * If we have allocated more blocks and copied less. We will have
> >> +	 * blocks allocated outside inode->i_size, so truncate them.
> >> +	 */
> >> +	if (pos + len > inode->i_size && ext4_can_truncate(inode))
> >> +		ext4_orphan_add(handle, inode);
> > 
> > I don't think we need this error handling here. For inline data we never
> > allocate any blocks so shorter writes don't need any cleanup.
> > 
> >> -	return copied;
> >> +	ret2 = ext4_journal_stop(handle);
> >> +	if (!ret)
> >> +		ret = ret2;
> >> +	if (pos + len > inode->i_size) {
> >> +		ext4_truncate_failed_write(inode);
> >> +		/*
> >> +		 * If truncate failed early the inode might still be
> >> +		 * on the orphan list; we need to make sure the inode
> >> +		 * is removed from the orphan list in that case.
> >> +		 */
> >> +		if (inode->i_nlink)
> >> +			ext4_orphan_del(NULL, inode);
> >> +	}
> > 
> > And this can go away as well...
> > 
> 
> Yeah, but if we don't call ext4_truncate_failed_write()->..->
> ext4_inline_data_truncate(), it will lead to incorrect larger i_inline_size
> and data entry. Although it seems harmless (i_size can prevent read zero
> data), I think it's better to restore the data entry(the comments need
> change later), or else it will occupy more xattr space. What do you think ?

Good point. I've found this out last time when I was reviewing your patches
and then forgot again. So please leave the code there but fix this
misleading comment:

/*
 * If we have allocated more blocks and copied less. We will have
 * blocks allocated outside inode->i_size, so truncate them.
 */

Something like:

/*
 * If we didn't copy as much data as expected, we need to trim back size of
 * xattr containing inline data.
 */

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR